1. Field of the Invention
The present invention relates to a fuel injection valve, in particular, a fuel injector for supplying fuel to a cylinder head or an intake manifold of a vehicle engine.
2. Description of Related Art
Conventionally, a fuel injection valve has been used for injecting and supplying fuel such as gasoline or light oil to a cylinder head of an engine. As shown in FIG. 6, the fuel injection valve 100 is provided at a lower part thereof with a housing pipe 101, a body valve 102 and an injection hole plate 103, as main components.
A valve needle 106 is inserted into an inner circumference of the housing pipe 101, which is formed in a hollow cylinder shape. An upper end of the body valve 102 is inserted into a lower end opening of the housing pipe 101. Circumferential surfaces of the housing pipe 101 and the body valve 102 in contact with each other are provided with a bonding portion 104 (as meshed in FIG. 6) formed by laser welding. The body valve 102 is formed in a hollow cylindrical shape. The body valve 102 is provided at an inner circumference thereof with a taper surface, whose diameter is smaller toward a lower end thereof, constituting a valve seat 105. The injection hole plate 103 is bonded to the lower end of the valve body 102. The injection hole plate 103, which is formed in a cup shape, is provided at a bottom wall thereof with injection holes 107.
When the valve needle 106, which is moved up and down reciprocatingly, is seated on the valve seat 105 of the valve needle 106, fuel is shut off. Accordingly, with respect to the valve seat 105, higher dimensional accuracy such as roundness accuracy and lower deformation are required.
However, the valve seat 105 of the conventional fuel injection valve 100 tends to be largely deformed, when the body valve 102 is bonded by laser welding to the lower end of the housing pipe 101.
The laser welding is performed in such a manner that, after the upper end of the body valve 102 is inserted into and comes in contact with the lower end of the housing pipe 101, laser beam is radiated so as to draw a circle from an outer circumferential side of the housing pipe 101 to circumferential surfaces of the body valve 102 and the housing pipe 101 in contact with each other. Welding heat is generated so as to draw a circle that follows a circular movement of the laser beam. The bonding portion 104 of the body valve 102 is sequentially heated and expands from time to time when the laser beam is radiated and, then, cooled and contracts. Since the welding heat is not uniformly generated, the body valve 102 in a vicinity of the bonding portion 104 is likely to be deformed so that the deformation thereof causes a deformation of the valve seat 105. In particular, when the deformation of the body valve 102 in a vicinity of the bonding portion 104 is not uniform circumferentially, the deformation of the valve seat 105 is more distinctive, which results in lowering a dimensional accuracy of the valve seat 105.
The lower dimensional accuracy of the valve seat 105, which is due to heat generating at the bonding portion 104, is caused by any heat bonding such as brazing, too.
The lower dimensional accuracy of the valve seat 105 causes a gap between the valve needle 106 and the valve seat 105 at a valve closing time and tends to leak fuel from the gap. Accordingly, Cxe2x80x94H chemical compounds such as CH4, that is, HC contents, in exhaust gas is likely to increase.
An object of the invention is to provide a fuel injection valve having a valve seat whose deformation due to bonding heat is smaller so that dimensional accuracy thereof is higher.
To achieve the above object, in a fuel injection valve having a housing pipe, a valve movable reciprocatingly and axially inside the housing pipe, and a body valve having a bottom wall constituting a valve seat with which the valve comes in contact and a side wall whose axial end is connected to a circumferential periphery of the bottom wall and whose the other axial end is fitted to and heat bonded to an end of the housing pipe, for example, by welding, the side wall is provided midway between the axial end and the other axial end thereof with a recess that is formed in advance before the body valve and the housing pipe are heat bonded to each other and serves to prevent a deformation of the side wall due to heat generated by the heat bonding from being straight transmitted to the valve seat.
Since the recess is provided in the side wall of the body valve, a deformation of the body valve due to heat generated by the heat bonding is partly absorbed by the recess so as not to transmit straight to the valve seat. Accordingly, the heat bonding does not lower a dimensional accuracy of the valve seat so much.
It is preferable that the recess is a ring shaped groove formed on an outer circumference of the side wall. The ring shaped groove serves to absorb a deformation of the body valve caused by press fitting the body valve to the housing pipe, since a bottom wall of the groove is operative like a plate spring.
More preferably, the ring shaped groove is located in a vicinity of a place where the body valve and the housing pipe are heat bonded to each other. In this case, a deformation area of the body valve between the ring shaped groove and the housing pipe is relatively small so that the ring shaped groove may effectively absorb the deformation.